The present invention is concerned with apparatus for producing finely divided liquid particles for household, industrial and medical spraying applications. The invention is particularly useful in the field of respiratory inhalation therapy.
A device that disperses liquid into a fine spray or aerosol, used for medical purposes, is often called a nebulizer. When the aerosol output from a nebulizer is conveyed to a patient through a flexible conduit or hose so that he can inhale the nebulizer output through either a face mask or a face tent, the patient is said to be receiving inhalation respiratory therapy. In other applications, the patient may be totally immersed in a mist tent so that his entire body, or at least the head and trunk, is surrounded by the aerosol. In still other cases, the patient may inhale the nebulizer output directly from a mouthpiece.
Until recently, there were only two means of producing aerosols for medical purposes. The Bernoulli principle was the first technique that was used, and most conventional pneumatic sprayers, atomizers and nebulizers utilize this principle. A substantial improvement was realized with the advent of the ultrasonic principle of atomization. While the ultrasonic nebulizer produces a superior aerosol as compared to conventional pneumatic systems, it is an expensive device using electronic components and thus may not be wholly dependable in service.
The most recent improvement uses what is now referred to as the Babington principle, descriptions of which can be found in U.S. Pat. Nos. 3,421,692, 3,421,699, 3,425,058, 3,425,059, 3,504,859 and 3,864,326. Some articles of interest describing utilization of this principle and its advantages in several publications include: The Babington Nebulizer: A New Principle for Generation of Therapeutic Aerosols by Mitchell Litt et al, appearing in the American Review of Respiratory Disease, Volume 105, Number 2, February 1972, pages 308-310; Popular Science, Clog-Proof Super Spray Oil Burner Saves Fuel Costs Two Ways by Norman Metzger, and appearing in Popular Science, January 1976, pages 64-67; and What Makes Coffee Coffee-er, Houses Cozier Breathing Easier, It's Superspray by Simon Dresner, and appearing in Popular Science, May 1973. Medical nebulizers that utilize the Babington principle are now being commercially used in the United States and parts of Europe.
Nebulizers employing the Babington principle provide flexibility in all of the important performance parameters such as operating flow range, nebulizer output capacity, and liquid particle size. Such nebulizers are also capable of producing an almost constant aerosol density throughout their wide range of operation. The flow range of atomized liquid plus gas may be varied from a minimum of about 5 liters per minute in one model to a maximum of about 300 liters per minute in another model. Output capacity of liquid vaporized in these units can also be varied from 0.2 cc/minute to 7 cc/minute. Since there are no moving or electronic parts to overheat, the mist is delivered at a cooler temperature which, in turn, provides for reduced condensation due to cooling on the walls of outlet conduits. Also, these nebulizers achieve optimum performance immediately, with no warm-up time required, an obvious advantage in a 15 to 20-minute treatment.
Clinicians generally agree that a particle size with a mass median diameter of 5 microns and below is the most beneficial from a therapeutic point of view. Nebulizers utilizing the Babington principle produce a spray wherein the liquid particle size falls within this desired range. Such nebulizers are easy to maintain and safe to use, particularly since they do not have any moving parts to wear out. They can also be quickly assembled and disassembled, and are safe to use with no chance of electrical malfunctions.